Art. 7. — K. Yaiuada : 



The mountiiig of the grating was of the usual Rowland type, 

 in wliich the grating and the photographic camera ran on rectan- 

 gular iron rails. The source of light in most cases was focussed on 

 the slit. by a lens. A quartz lens was used for the photographing 

 of the ultra-violet region. The focal length of the lens was about 

 12 cm. and its diameter 5 cm. For the visible region, it was found 

 profitable to use a short focus cylindrical glass lens together with a 

 spherical one, in order to condense the light. To analyse the 

 nature of the vibration in the magnetic field, a Wollaston or 

 Rochon quartz prism was introduced between the lens and the 

 slit. The optical arrangement is shown in Fig. 3. 



The spectra produced Ijy the Rowland grating almost always 

 give rise to ''ghosts," to whicli 1 liave paid special attention. 

 The distance A of the ghost from the main line 

 divided by its wave-length X, i. e. -y- is constant 

 for different orders of spectra'-* with respect to 

 the instrument. Hence this constant is ser- 

 viceable to decide the wave-length when its 



SLi 



C\tU.nJUicaJL oC*»ui. 



O TMaJ^^ 



order is known. In our graring -y- =2*568 x 



In this experiment, I succeeded in plioto- 

 graphing as far as the fifth order spectra, by 

 using a glass and a quartz lens separately to 

 take the same region of the spectra. To 

 distinguish between iron and nickel lines, the 



1) Itowlaud, Physical Papers, p. 536 (1902) Baltimore. 



